Use of syntactic foams as core materials gives several distinct advantages over traditionally used core materials. Syntactic foams have an excellent combination of compressive strength, low density, low radar detectability and low moisture absorption coefficient among others. The present work aims at studying the behavior of sandwich-structured composites containing syntactic foam as core material under three-point bending conditions. Flexural and short-beam shear tests are conducted, where large (16 : 1) and small (5 : 1) aspect ratio (span length/thickness Downloaded from ratio) specimens are tested, respectively. It is observed that the specimen failure mode changes completely with the change in the aspect ratio. Specimens are found to fracture under the effect of shear stresses in the smaller aspect ratio specimens, whereas compressive stresses lead to the fracture in higher aspect ratio specimens. The observations of fracture features are correlated with the test data and the loaddisplacement curves obtained in the tests. A method of analysis is also presented for syntactic foams and the sandwich structures containing syntactic foam as core material.
Neat epoxy (NE) and epoxy system with different volume fractions of fly ash fillers with their surfaces treated by silane bearing material were made and the responses to exposure by immersion in varying aqueous media, such as plain water (PW), seawater (SW) and seawater containing small amount of dilute hydrochloric acid (SWA) maintained at 80 C, established through weight measurements recorded up to 100 h on the test coupons. Further on, the 100 h exposed samples were subjected to compression tests to evaluate the strength. The results showed that both NE and the silane treated ash bearing composites generally exhibited the highest water absorption in SWA case and the lowest in SW media, with the water absorption level for PW case falling in between. When the ash content in the composite is very large, the water absorption levels tend to be lower for both SW and SWA. The data further showed that unexposed samples recorded less strength compared to the exposed ones. In the case of exposed samples, in all the media employed, as the ash content increases the strength also increases. Further, it was noticed that the samples exposed to SW showed higher strength than the corresponding values noticed with SWA case. Lower strength was found in samples immersed in PW case. Attempts to explain these differing trends are made in this effort by analyzing the features observed on the surface of compression failed samples using fractography technique employing scanning electron microscope (SEM).
Compressive properties of fly ash-epoxy composites with and without exposure to warm water were studied. Ash by itself being susceptible to absorption of water the amount of fly ash was found to influence the water absorption. Composites tested under compression after two durations of exposure showed improvement in properties. Properties after longer exposure were, however, not much different from those recorded for shorter exposed test samples. The microscopic examination revealed less of debonds at the ash-epoxy interface consequent to water ingress. This is interpreted in this work to mean that ash particles absorbing water and attendant swelling could have aided in this situation which factor could also be augmented by the epoxy showing signs of volumetric expansion following ingress of water. These situations could have helped in reduction of the severity of these debonds acting as stress raisers thereby improving the compressive properties of water ingressed composites.
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